1. Field of the Invention
The present invention relates to a manufacturing method of a semiconductor device and, more particularly, to a manufacturing method of a semiconductor device having a capacitor.
2. Description of the Related Art
As the nonvolatile memory that can still store the information after the power supply is turned off, the flash memory and the ferroelectric memory (FeRAM) are known.
The flash memory has a floating gate that is buried in a gate insulating film of the insulated-gate field effect transistor (IGFET), and stores the information by accumulating a charge indicating the stored information in the floating gate. A tunnel current that passes through the gate insulating film must be supplied to write/erase the information, and thus a relatively high voltage is required.
The FeRAM has a ferroelectric capacitor that stores the information by utilizing a hysteresis characteristic of a ferroelectric substance. The ferroelectric film formed between the upper electrode and the lower electrode in the ferroelectric capacitor generates a polarization in response to a voltage applied between the upper electrode and the lower electrode, and has a spontaneous polarization that still holds the polarization even after the applied voltage is removed.
If the polarity of the applied voltage is inverted, the polarity of the spontaneous polarization is also inverted. The information can be read by sensing the polarity and the magnitude of this spontaneous polarization. The FeRAM has such an advantage that such FeRAM can be operated at a low voltage rather than the flash memory and also a high-speed writing can be attained with low power consumption.
As the structure of the capacitor used in the memory cell of the FeRAM, the structure in which the Pt thin-film electrode, the PZT ferroelectric film, and the upper electrode are formed sequentially on the amorphous SiO2 directly or via the buffer layer such as Ti, Ta, or the like on the Si substrate is set forth in following Patent Literature 1, for example.
In the prior art, in the case where a film such as Ti, or the like having the self-orientation characteristic is to be formed on the insulating film, method of changing the kind of gas when forming Ti is usually employed as a measure for improving the orientation of the film.
For instance, the method of adding H2O during the Ti sputter is set forth in following Non-Patent Literature 1. In Non-Patent Literature 1, there is shown experimental results that increase a (002) orientation intensity of the Ti film by adding H2O during the Ti sputter.
[Patent Literature 1]                Patent Application Publication (KOKAI) Hei 9-53188 (page 3, FIG. 1)        
[Non-Patent Literature 1]                Jpn. J. Appl. Phys. Vol.36(1997) pp.L154–L157 part 2, No.2A, 1 Feb. 1997        
However, according to such Ti-film forming method, it may be considered that since H2O is always present in the surrounding atmosphere of the Ti film during the sputter, it is difficult to get a pure film quality.
In Non-Patent Literature 1, it is also studied to form Ti film by introducing H2O only at the initial stage of the film formation, and subsequently form the Ti film without introducing H2O. It is argued in Non-Patent Literature 1 that this method improves the quality of Ti film of later stage.
However, since H2O remains in an inside of Ti-film forming chamber for a while even after shutting of the introduction of H2O, it is impossible to perfectly avoid the mixture of H2O into an upper portion of the Ti film.
Also, since a reactive gas (H2O) is adhered to the Ti target, it is considered that the influence remains for a long time. Thus, a surface reforming of the target is caused by the reactive gas (H2O) that was adhered to the target. Therefore, when the number of sheets of the processed wafer on which Ti is formed is increased, it is uncertain whether or not the Ti film with the same film quality can be supplied.
As other anxious points, the dark-space shielding portion is covered with the insulator (Ti oxide) to cause the abnormal discharge when H2O is introduced into the chamber. Thus, there arises possibility that the stable plasma cannot be maintained in the chamber.
In addition, in Non-Patent Literature 1, the SiO2 surface is terminated by the O—H bond. Since the O—H bond itself is unstable and also presence of one Si—OH group to ten Si—O groups is stable on the surface, it is difficult to increase the density of hydrogen termination on the surface of the insulating film. In this case, the Ti film is oxidized by H2O.